Frame rates: 3D view port vs VSE
In 3d view you may be playing only the OpenGL version of the scene, for example in textured or material mode or even just wireframe. Blender is optimised for this and it takes relatively little memory. This will play very fast.

After rendering to a high resolution image sequence you are asking Blender to load into memory a lot more data to display. Try selecting the strip and and creating a proxy, define the resolution and timecode type in the strip properties panel. The rebuild proxy/TC function is in the Strip menu at the bottom of the VSE timeline. Then go to the VSE preview window properties (N-key) and select the proxy size to view. Proxies of your footage should play back properly (less memory and processing overhead).

Alternatively go to the Blender timeline (not the VSE) and change the playback mode to AV-Sync. This will prioritise playback to frame rate and drop frames to do so.